The Thermocouple is The Most Widely used Transducer For Temperature Measurement. A Thermocouple is Device That Converts Thermal Energy Directly Into An Electric Voltage When a Temperature Gradient Exits Between The Two End Junction Of a Pair of Two Dissimilar Metal Wires.
Classification of Thermocouple:
1. T type thermocouple;
2.P type thermocouple;
3. S type
thermocouple;
4. K type
thermocouple;
5. J type
thermocouple;
6. N type
thermocouple.
TYPE K THERMOCOUPLE
-270..1370 DEG
C
PRINCIPLE OF THERMOCOUPLE
•
Seeback Discovered in 1821 The Existence of
Thermo Electric Currents While Observing Electro-magnetic Effects Associated
With Bismuth-Copper& Bismuth- Antimony Circuits. His Experiments Showed
That, When The Junctions of Two Dissimilar Metals Forming a Closed Circuit Are
Exposed To Different Temperatures, A New Thermal Electromotive Force Generated
Which Induces a Continuous Electric Current.
•
The seeback effect concern the net conversion
of thermal energy into electric energy with the appearance of an electric
current. The seeback voltage refers to the net thermal electromotive force
(EMF) set up in a thermocouple under zero current conditions. The direction and
magnitude of the seeback voltage ES depend on the temperatrure of the junction
and on the materials making up the thermocouple.
Thermistors (THERMAL RESISTORS)
act in much
the same way as RTDs, but use a semiconductor device to change resistance
rather than a metallic element. They have their own characteristics in the
group:
•Narrowest measuring range, by far;
•Lowest stability and linearity;
•Accuracy and response time comparable to thermocouples;
•Highest sensitivity;
•Least expensive; and
•Robust signal.
If the application isn't too critical and within the
temperature limitations, thermistors can be an appropriate choice
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